Endurance training: is it bad for you?

Abstract

To illustrate the characteristics of endurance exercise training and its positive effects on health.To provide an overview on the effects of endurance training on airway cells and bronchial reactivity.To summarise the current knowledge on respiratory health problems in elite athletes. Endurance exercise training exerts many positive effects on health, including improved metabol-ism, reduction of cardiovascular risk, and reduced all-cause and cardiovascular mortality. Intense endurance exercise causes mild epithelial injury and inflammation in the airways, but does not appear to exert detrimental effects on respiratory health or bronchial reactivity in recreational/non-elite athletes. Conversely, elite athletes of both summer and winter sports show increased susceptibility to development of asthma, possibly related to environmental exposures to allergens or poor conditioning of inspired air, so that a distinct phenotype of "sports asthma" has been proposed to characterise such athletes, who more often practise aquatic and winter sports. Overall, endurance training is good for health but may become deleterious when performed at high intensity or volume.

Figure 1

a) Bronchial epithelial cell counts in induced sputum significantly increased post-race. **: p<0.01. b) IL-8 concentration in sputum supernatants was positively correlated with bronchial epithelial cell absolute counts post-race. Oct, May and Nov refer to three different half-marathon races during which samples were collected. Reproduced from [15] with permission.

Figure 2

Apoptosis of bronchial epithelial cells in post-race samples. a) Airway cell composition (Diff-Quick staining) and apoptosis (TdT-mediated dUTP nick end labelling (TUNEL)) of airway cells in induced sputum at baseline and after a half-marathon race. b) A large proportion of bronchial epithelial cells were apoptotic in post-race samples. Oct, May and Nov refer to three different half-marathon races during which samples were collected. **: p<0.01. Reproduced from [15] with permission.

Figure 3

Mechanisms responsible for epithelial injury and influx of neutrophils into the airways during endurance exercise. Reproduced and modified from [18] with permission.

Figure 4

All-cause and cardiovascular mortality according to running quintiles. MET: metabolic equivalent. Reproduced from [5] with permission.